Melt butter in a medium saucepan over low heat; add onion, and cook until tender.
Place plums and plum juice in container of an electric blender; process until smooth . Add pureed plums to onion. Stir in lemonade , chili sauce , soy sauce, 1 tablespoon salt, mustard, Worcestershire sauce, ginger, and hot sauce . Cook , uncovered , over low heat 15 minutes, stirring occasionally. Remove from heat; set aside to cool . Cover and refrigerate sauce overnight.
Cut ribs into serving - size pieces (3 to 4 ribs per person). Place ribs , 1 tablespoon salt, and water to cover in a large stockpot. Bring to a boil; cover and simmer over medium heat 45 minutes or until ribs are tender. Drain well.
Place ribs, bone side down, on grill over slow coals. Grill 10 minutes; turn meaty side down, and cook until browned. Brush sweet-and-sour sauce on both sides of the ribs, and cook 5 minutes on each side. Serve any remaining sauce with ribs .